The present invention relates to a semiconductor component. In one embodiment, a semiconductor component is provided, having a soft diode behavior.
For a fast and low-loss switching behavior, the behavior of semiconductor structures is intended to proceed such that it is as “soft” as possible. The semiconductor component can be an IGBT with backward diode.
The description is given on the basis of an IGBT, but this does not signify any restriction. Rather, a “semiconductor component” can also be understood to mean for example a combination of an IGBT with a MOSFET or a Schottky diode.
For an IGBT which can be operated in a diode operating mode and in an IGBT operating mode, a diode operating mode can usually take place in opposite polarity with respect to the actual IGBT operating mode.
IGBTs configured in this way with RC-IGBT structures (reverse conducting IGBT structures) upon turn-on initially operate in a MOSFET operating mode, that is to say in a unipolar operating mode, in which no hole injection takes place from the rear side of the semiconductor body. It is only at higher currents that the rear-side p-conducting emitter zone turns on, such that holes are injected into the drift path and the semiconductor component then operates in the IGBT operating mode, that is to say a bipolar operating mode.
The changeover from the unipolar operating mode to the bipolar operating mode takes place when the electrons, which are the sole charge carriers of the current in the unipolar operating mode in the drift path and which flow away upstream of the p-conducting emitter zones transversely to the nearest n-conducting zone, produce an ohmic voltage drop upstream of the p-conducting emitter zones, which voltage drop excites the p-conducting emitter zones to effect a hole injection. The voltage drop must be approximately 0.7 V at room temperature.
This can mean that the current at which the changeover from the unipolar operating mode to the bipolar operating mode takes place can depend on the doping of the rear-side n-conducting emitter zones within the p-type emitter zones and can moreover likewise depend appreciably on the geometrical arrangement of the p-conducting and/or the n-conducting emitter zones: the greater the distance from one n-conducting zone to the next n-conducting zone on the rear side of the semiconductor body, the smaller the current possibly becomes which is required to produce the voltage drop of approximately 0.7 V.
It can follow from this that p-conducting emitter zones that are as wide as possible can be expedient for good on-state properties of the semiconductor component.
Simply enlarging the p-type zones can lead to widely distributed n-type zones, however. It may be desirable for the latter to be as close to one another as possible in order to be able to utilize the corresponding volume of the cell region of the semiconductor body or the corresponding cross-sectional region thereof for the diode operating mode.
The requirement of good on-state properties of the semiconductor component on account of wide p-conducting zones and n-conducting zones that are close together for a high current flow in the diode operating mode apparently cannot readily be fulfilled simultaneously with the requirements made with regard to a high diode softness or a low switching power loss.
One possibility for obtaining a soft diode behavior may be to reduce the local charge carrier lifetime near the front-side anode of the integrated diode. The anodal carrier flooding can thereby be reduced, which results in an increased diode softness. What is more, the reverse current peak and the total storage charge are reduced. However, this method has the effect that the collector-emitter saturation voltage VCESat increases as the reduction of the charge carrier lifetime increases. As a result, the degree of charge carrier lifetime reduction is limited since the on-state losses also increase with the increase of VCESat, which can lead to an excessively great heating of the semiconductor component.
A further approach for improving the diode softness may be to increase the doping concentration of the rear-side n-type emitter zone. The rear-side carrier flooding thereby increases, which increases the softness. However, this can in turn result in an increase in the storage charge and, consequently, in increasing switching losses of the diode and in increasing turn-on losses of the IGBT.
For these and other reasons, there is a need for the present invention.